This invention relates to the recirculation of hydrogen containing anode effluent discharged from a fuel cell stack of a fuel cell power plant.
Tokuhyo Hei 10-511497 published by the Japanese Patent Office in 1998 discloses a mechanism that recirculates hydrogen containing anode effluent discharged from an anode of a fuel cell stack, to a hydrogen supply passage that supplies hydrogen to the anode of the fuel cell stack. The mechanism comprises an ejector provided in the hydrogen supply passage and a recirculation passage connected thereto.
A hydrogen source supplies hydrogen to the anode via the hydrogen supply passage under a predetermined pressure. The ejector aspirates anode effluent in the recirculation passage into the hydrogen supply passage due to Venturi effect of the flow of hydrogen in the hydrogen supply passage.
The recirculation flowrate of the anode effluent therefore depends on the hydrogen flowrate in the hydrogen supply passage, and when the hydrogen flowrate is small, the ejector is not able to exert sufficient suction force over the anode effluent in the recirculation passage. If an ejector of smaller size is applied, it may be possible to aspirate anode effluent even when the hydrogen flowrate in the hydrogen supply passage is small. However, such a small ejector cannot pass the required amount of hydrogen when the fuel stack is in the full operation.
In other words, the ejector efficiently works only when the hydrogen flowrate in the hydrogen supply passage is within a predetermined flowrate range. A fuel cell power plant, when used for a vehicle drive system, is apt to suffer a large variation of loads depending on the vehicle running conditions, and the hydrogen flowrate in the hydrogen supply passage also varies largely. In such a fuel cell power plant, the anode effluent recirculation system using an ejector works only in limited conditions.
It is therefore an object of this invention to improve the performance of an anode effluent recirculation system using an ejector.
In order to achieve the above object, this invention provides a fuel cell power plant comprising a fuel cell stack that generates an electric power by a reaction of hydrogen and air, and discharges a hydrogen containing anode effluent, a hydrogen supply passage that supplies hydrogen to the fuel cell stack, a recirculation passage connected to the fuel cell stack to recirculate the anode effluent to the hydrogen supply passage, an ejector that promotes a recirculation of the anode effluent by exerting a suction force on the anode effluent in the recirculation passage depending on a flow velocity of hydrogen in the hydrogen supply passage, and a recirculation pump installed in the recirculation passage to pressurize the anode effluent.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.